The recent publication of a study conducted by Facebook, which manipulated the amount of positive or negative material that users saw in their Facebook newsfeeds, has provoked much critical comment (1). The goal was to see whether the emotional content of users' newsfeeds affected their emotional states, as measured by their posts (2).

The study involved approximately 700 000 Facebook users (2), none of whom were asked to consent (3). Most published discussion has been about Facebook's manipulation of users without their permission. Facebook's position, stated in the paper, is that no specific consent was needed because the terms of service to which users agree when registering for Facebook allow it to do this research (2). This assertion is dubious—Facebook's terms of service at the time of the study stated that it could employ data from its users for various purposes but do not mention intentional manipulation of information provided to users in ways that are not directly helpful to them (3).